Given an integer , return if it is a power of four. Otherwise, return . n true false An integer is a power of four, if there exists an integer such that . n x n == 4x Example 1: Input: n = 16
Output: true Example 2: Input: n = 5
Output: false Example 3: Input: n = 1
Output: true Solution: The easiest way how to solve this problem is to  divide N on 4 and that is it. We will iterate again and again till our number is bigger than 1. public boolean isPowerOfFour(int n) {
    if (n == 0){
        return false;
    }
    
    while(n != 1){
        if (n % 4 != 0){
            return false;
        }
        n /= 4;
    }
    return true;
} But also we can use recursion: public boolean isPowerOfFour(int n) {
        return check(n, 1);
    }

    boolean check(int n, long value) {
        if (value >= n) return n == value;

        return check(n, value * 4);
    } And sure, we can solve it with math, but I don’t want to share it with you. Because for me, you usually cannot find a mathematical solution without solving this problem before. Does it clear? Write your comments. ok ok and out next problem for today Reverse Vowels of a String Given a string , reverse only all the vowels in the string and return it. s The vowels are , , , , and , and they can appear in both cases. 'a' 'e' 'i' 'o' 'u' Example 1: Input: s = "hello"
Output: "holle" Example 2: Input: s = "leetcode"
Output: "leotcede" Solution: To solve this problem, we will use the popular technique of two-pointers. The main idea of solving problems like this -- is to understand base techniques and use them later in medium and hard problems. We are going to prepare a vowel dictionary. Then we can iterate in both directions. If both pointers stay on the vowels we can swap them. And continue our direction. public String reverseVowels(String s) {
    Set<Character> dict = new HashSet<>();
    dict.add('a');
    dict.add('A');
    dict.add('e');
    dict.add('E');
    dict.add('i');
    dict.add('I');
    dict.add('o');
    dict.add('O');
    dict.add('u');
    dict.add('U');

    int reader = 0;
    int writer = s.length() - 1;

    StringBuilder sb = new StringBuilder(s);
    while (reader < writer) {
        if(!dict.contains(s.charAt(reader))){
            reader ++;
        }
        if (!dict.contains(s.charAt(writer))){
            writer--;
        }
        if (dict.contains(s.charAt(reader)) && dict.contains(s.charAt(writer))){
            char tmp = s.charAt(reader);
            sb.setCharAt(reader++, s.charAt(writer));
            sb.setCharAt(writer--, tmp);
        }
    }
    return sb.toString();
} Does it clear? Write your comments.

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Power of Four and Reverse Vowels of a String

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